The present invention relates to a microfluidic device, which can be interfaced to a mass spectrometer (MS). The device comprises a microchannel structure having a first port (inlet port) and a second port (outlet port). A sample to be analysed is applied to the first port and presented to the mass spectrometer in the second port. This second port will be called an MS-port. There may be additional inlet and outlet ports. During passage through the microchannel structure the sample is prepared to make it suitable for analysis by mass spectrometry.
The sample presented in an MS-port will be called an MS-sample. An analyte in an MS-sample is an MS-analyte. xe2x80x9cSamplexe2x80x9d and xe2x80x9canalytexe2x80x9d without prefix will primarily refer to a sample applied to an inlet port.
One important aspect of the present invention concerns mass spectrometry in which the MS-samples are subjected to Energy Desorption/Ionisation from a surface by input of energy. Generically this kind of process will be called EDI and the surface an EDI surface in the context of the invention. Typicallly EDIs are thermal desorption/ionisation (TDI), plasma desorption/ionisation (PDI) and various kinds of irradiation desorption/ionisation (IDI) such as by fast atom bombardment (FAB), electron impact etc. In the case a laser is used the principle is called laser desorption/ionisation (LDI). Desorption may be assisted by presenting the MS analyte together with various helper substances or functional groups on the surface. Common names are matrix assisted laser desorption/ionisation (MALDI) including surface-enhanced laser desorption/ionisation (SELDI). For MALDI see the publications discussed under Background Publications below. For SELDI see WO 0067293 (Ciphergen Biosystems).
The surface from which desorption/ionisation is intended to take place is called an EDI surface.
By microformat is meant that in least a part of the microchannel structures the depth and/or width is in the microformat range, i.e.  less than 103 xcexcm, preferably  less than 102 xcexcm. In the most typical microformat structures either the width and/or the depth are in principle within these ranges essentially everywhere between the sample inlet port and the MS-port.
For some time there has been a demand for microfluidic sample handling and preparation devices with integrated MS-ports. This kind of devices would facilitate automation and parallel experiments, reduce loss of analyte, increase reproducility and speed etc.
WO 9704297 (Karger et al) describes a microfluidic device that has an outlet port that is claimed useful when conducting electrospray ionisation mass spectrometry (ESI MS), atmospheric pressure chemical ionisation mass spectrometry (APCI MS), matrix assisted laser desorption/ionisation mass spectrometry (MALDI MS) and a number of other analytical principles.
U.S. Pat. No. 6,110,343 (Ramsey et al) describes an electrospray interface between a microfluidic device and a mass spectrometer.
U.S. Pat. No. 5,969,353 (Hsieh) describes an improved interface for electrospray ionization mass spectrometry. The interface is in the form of an electrospray tip connected to a microchannel structure of a chip.
U.S. Pat. No. 5,197,185 (Yeung et al) describes a laser-induced vaporisation and ionization interface for directly coupling a microscale liquid based separation process to a mass spectrometer. A light-adsorbing component may be included in the eluting liquid in order to facilitate vaporisation.
U.S. Pat. No. 5,705,813 (Apffel et al) and U.S. Pat. No. 5,716,825 (Hancock et al) describe a microfluidic chip containing an interface between a microfluidic device and an MALDI-TOF MS apparatus. The microfluidic device comprises
(a) an open ionisation surface that may be used as the probe surface in the vaccum gate of an MALDI-TOF MS apparatus (column 6, lines 53-58 of U.S. Pat. No. 5,705,813) or
(b) a pure capture/reaction surface from which the MS-analyte can be transferred to a proper probe surface for MALDI-TOF MS (column 12, lines 13-34, of U.S. Pat. No. 5,716,825).
These publications suggest that means, such as electrical connections, pumps etc, for transporting the liquid within a microchannel structure of the device are integrated with or connected to the device. This kind of transporting means imposes an extra complexity on the design and use, which in turn may negatively influence the production costs, easiness of handling etc of these devices.
U.S. Pat. No. 5,705,813 (Apffel et al) and U.S. Pat. No. 5,716,825 (Hancock et al) are scarce about
the proper fluidics around the MALDI ionisation surface,
the proper crystallisation on the MALDI ionisation surface,
the proper geometry of the port in relation to crystallisation, evaporation, the incident laser beam etc,
the proper arrangement of conductive connections to the MALDI ionisation surface for MALDI MS analysis.
WO 04297 (Karger et al) and WO 0247913 (Gyros AB) suggest to have microchannel structures in radial or spoke arrangement.
A number of publications referring to the use of centrifugal force for moving liquids within microfluidic systems have appeared during the last years. See for instance WO 9721090 (Gamera Bioscience), WO 9807019 (Gamera Bioscience) WO 9853311 (Gamera Bioscience), WO 9955827 (Gyros AB), WO 9958245 (Gyros AB), WO 0025921 (Gyros AB), WO 0040750 (Gyros AB), WO 0056808 (Gyros AB), WO 0062042 (Gyros AB) and WO 0102737 (Gyros AB) as well as WO 0147637 (Gyros AB), WO 0154810 (Gyros AB), WO 0147638 (Gyros AB), and WO 0146465.
See also Zhang et al, xe2x80x9cMicrofabricated devices for capillary electrophoresisxe2x80x94electrospray mass spectrometryxe2x80x9d, Anal. Chem. 71 (1999) 3258-3264) and references cited therein.
Kido et al., (xe2x80x9cDisc-based immunoassay microarraysxe2x80x9d, Anal. Chim. Acta 411 (2000) 1-11) has described microspot immunoassays on a compact disc (CD). The authors suggest that a CD could be used as a continuous sample collector for microbore HPLC and subsequent detection for instance by MALDI MS. In a preliminary experiment a piece of a CD manufactured in polycarbonate was covered with gold and spotted with a mixture of peptides and MALDI matrix.
A first object is to provide improved means and methods for transporting samples, analytes including fragments and derivatives, reagents etc in microfluidic devices that are capable of being interfaced with a mass spectrometer.
A second object is to provide improved microfluidic methods and means for sample handling before presentation of a sample analyte as an MS-analyte. Sub-objects are to provide an efficient concentration, purification and/or transformation of a sample within the microfluidic device while maintaining a reproducible yield/recovery, and/or minimal loss of precious material.
A third object is to provide improved microfluidic methods and means that will enable efficient and improved presentation of the MS-sample/MS-analyte. This object in particular applies to MS-samples that are presented on a surface, i.e. an EDI surface.
A fourth object is to enable reproducible mass values from an MS-sample that is presented on a surface, i.e. on an EDI surface.
A fifth object is to provide improved microfluidic means and methods for parallel sample treatment before presentation of the analyte to mass spectrometry. The improvements of this object refer to features such as accuracy in concentrating, in chemical transformation, in required time for individual steps and for the total treatment protocol etc. By parallel sample treatment is meant that two or more sample treatments are run in parallel, for instance more than five, such as more than 10, 50, 80, 100, 200, 300 or 400 runs. Particular important numbers of parallel samples are below or equal to the standard number of wells in microtiter plates, e.g. 96 or less, 384 or less, 1536 or less, etc
A sixth object is to provide a cheap and disposable microfluidic device unit enabling parallel sample treatments and having one or more MS-ports that are adapted to a mass spectrometer.
The present inventors have recognized that several of the above-mentioned objects can be met in the case inertia force is used for transportation of a liquid within a microfluidic device of the kind discussed above. This is applicable to any liquid that is used in the microfluidic device, for instance washing liquids and liquids containing at least one of (a) the analyte including derivatives and fragments thereof, (b) a reagent used in the transformation of the sample/analyte, etc.
The present inventors have also recognized that one way of optimizing an EDI area within a microfluidic device is related to
(a) the design and/or positioning of a conducting layer in the EDI area, and/or
(b) the importance of a conductive connection to the EDI area for MS analysis.
This kind of connection supports the proper voltage and/or charge transport at the EDI area, for instance.
Improper conductive properties may interfere with the mass accuracy, sensitivity, resolution etc.
Conductive and non-conductive properties shell refer to the property of conducting electricity.
A first aspect of the invention is thus a method for transforming a liquid sample containing an analyte to an MS-sample containing an MS-analyte and presenting the MS-sample to a mass spectrometer. The method is characterized in comprising the steps of:
(a) applying the liquid sample to an inlet port of a covered microchannel structure of a microfluidic device,
(b) transforming the liquid sample to an MS-sample containing the MS-analyte within the microchannel structure, and
(c) presenting the MS-analyte to the mass spectrometer.
A further characteristic feature of this aspect is that transport of liquid within the microchannel structure is performed by the application of inertia force. Inertia force may be the driving force in only a part of the microchannel structure or the whole way from an inlet port to an MS-port and/or to any other outlet port. It is believed that the most general and significant advantages of using inertia force will be accomplished in so called transporting zones, i.e. between zones having predetermined functionalities, or for overcoming or passing through valve functions within a microchannel structure (capillary junctions, hydrophobic breaks etc). See below. The MS-port typically has a conductive connection for MS analysis.
At the priority date the most important inertia force for microfluidic devices is centrifugal force. In other words a force that causes outward radial transportation of liquid by spinning a disc in which the liquid is located within microchannel structures that are oriented radially (spinning is around an axis that is perpendicular to the plane of the disc). Inertia force caused by other changes of direction and/or magnitude of a force can be utilized.
The first aspect also includes the corresponding mass spectrometric method, i.e. the same method together with the actual collection of a mass spectrum and analysis thereof, for instance in order to gain molecular weight and structure information about the analyte.
The first aspect is further defined as discussed below for the microfluidic device as such and for the individual steps.
A second aspect of the invention is a microfluidic device containing one, two or more microchannel structures containing an inlet port, an MS-port and a flow path connected to one or both of the ports. The device may be disc-formed or otherwise provide a planar form. The characteristic feature is that the microchannel structures are oriented radially in an annular/circular arrangement. Thus each microchannel structure extends in a radial direction with an inlet port at an inner position and an outlet port such as an MS-port, at an outer peripheral position. The MS-port typically has a conductive connection as discussed above. The features discussed below further define this aspect of the invention.
A third aspect of the invention is a microfluidic device comprising a plurality of covered microchannel structures as defined herein and with each microchannel structure having an MS-port comprising an EDI area in which there is a conducting layer (layer I). This aspect of the present invention comprises a number of subaspects having the common characteristic feature that there may be a conductive connection to layer (I) of each individual EDI area, as discussed above. There are also features that are distinct for each subaspect.
A first subaspect is further characterized in that layer (I) of each EDI area is part of a continuous conducting layer that is common for two or more up to all of the EDI-areas.
A second subaspect is further characterized in that in each EDI area there is a non-conducting layer (layer II) between layer (I) and the surface of the EDI area. Layer (II) in each EDI area may be part of a continuous non-conducting layer that is common for two or more up to all of the EDI-areas.
A third subaspect is further characterised in that each MS-port has an opening that is restricted by a lid which is common for and covers a number of microchannel structures. The lid may have a conducting layer that at least embraces the openings that are present in the lid. The conducting layer may be continuous in the sense that it covers at least the areas around and between the openings of two or more up to all of the MS-ports. This layer may have a conductive connection as discussed above.
A fourth subaspect is similar to the third subaspect in the sense that there is a lid covering at least a part of each microchannel structures. In this subaspect the lid also covers or restricts the openings of the MS-ports and is removable to an extent that enables exposure of the opening in each MS-port, for instance exposing the surfaces of EDI areas. For EDI ports the removal will facilitate irradiation and the desorption/ionisation of the MS-analyte. The removal may also facilitate evaporation of volatile components.
The Sample
The sample applied to an inlet port may contain one or more analytes, which may comprise lipid, carbohydrate, nucleic acid and/or peptide structure or any other inorganic or organic structure. The sample treatment protocol to take place within the microchannel structure typically means that the sample is transformed to one or more MS-samples in which
(a) the MS-analyte is a derivative of the starting analyte and/or
(b) the amount(s) of non-analyte species have been changed compared to the starting sample, and/or
(c) the relative occurrence of different MS-analytes in a sample is changed compared to the starting sample, and/or
(d) the concentration of an MS-analyte is changed relative the corresponding starting analyte in the starting sample, and/or
(e) sample constituents, such as solvents, have been changed and/or the analyte has been changed from a dissolved form to a solid form, for instance in a co-crystallised form.
Item (a) includes digestion into fragments of various sizes and/or chemical derivatization of an analyte. Digestion may be purely chemical or enzymatic. Derivatization includes so-called mass tagging of either the starting analyte or of a fragment or other derivative formed during a sample treatment protocol, which takes place in the microchannel structure. Items (b) and/or (c) include that the sample analyte has been purified and/or concentrated. Items (a)-(d), in particular, apply to analytes that are biopolymers comprising carbohydrate, nucleic acid and/or peptide structure.
The sample is typically in liquid form and may be aqueous.
The sample may also pass through the microchannel structure without being changed. In this case the structure only provide a proper form for dosing of the analyte to the mass spectrometer.